Graphene represents an atomically thin layer of carbon in which the carbon atoms reside at regular two-dimensional lattice positions within a single sheet or a few stacked sheets (e.g., about 10 or less) of fused six-membered carbon rings. In its various forms, this material has garnered widespread interest for use in a number of applications, primarily due to its favorable combination of high electrical and thermal conductivity values, good mechanical strength, and unique optical and electronic properties. Of particular interest to industry are large-area graphene films for applications such as, for example, special barrier layers, coatings, large area conductive elements (e.g., RF radiators or antennas), and flexible electronics. A number of contemplated graphene applications have also been proposed for carbon nanotubes, since these two materials have certain properties that are comparable to one another. However, an advantage of graphene over carbon nanotubes is that graphene can generally be produced in bulk much more inexpensively than can the latter, thereby addressing perceived supply and cost issues that have been commonly associated with carbon nanotubes.
Despite the fact that graphene is generally synthesized more easily than are carbon nanotubes, there remain issues with production of graphene in quantities sufficient to support various commercial operations. Scalability to produce large area graphene films represents a particular problem. The most scalable processes developed to date for making graphene films utilize chemical vapor deposition (CVD) technology. In typical CVD processes, a carbon-containing gas is decomposed at high temperatures into various reactive carbon species, which then deposit upon a suitable growth catalyst and reorganize to form a graphene film. In typical CVD graphene syntheses, a carbon-containing gas and a copper-containing substrate are heated to a high temperature (e.g., about 900° C.-1000° C.) that is just below the melting point of the copper (i.e., 1061° C.). Both metallic copper substrates and copper-coated substrates can be used (e.g., nickel or silicon carbide substrates coated with copper). The CVD growth process can take place at either atmospheric pressure or a sub-atmospheric pressure. Due to the high temperatures employed in typical CVD processes, as well as the common use of reduced pressures during growth, scaling to afford graphene growth over large substrate areas can be expensive and complex. Further, since CVD growth processes often operate in the near-melting point regime of the substrate, substrate deformation can commonly occur, which can be undesirable for precision applications. CVD growth of graphene may not be possible at all on certain low melting substrates.
In view of the foregoing, improved processes for producing bulk quantities of graphene, particularly deposition of graphene films over a large surface area, would represent a substantial advance in the art. The present disclosure satisfies the foregoing need and provides related advantages as well.